27 synthesis, mode of action and regulatory effects of thyroid hormone Flashcards
what is the thyroid follicle
a small spherical group of cells containing a cavity
what do follicular cells secrete
thyroid hormones
what do C-cells secrete
calcitonin
is colloid a glycoprotein
yes
what does the thyroid gland produce
- T3 and T4 hormones
- calcitonin
why must sufficient iodine be taken in to maintain thyroid hormone synthesis
as T3 and T4 incorporate iodine
is iodine more concentrated in the follicular cells or the plasma
the follicular cells, 20-50x more
what does the sodium/iodine symporter do
transport 2Na+ for every iodine ion
what does the Na+ electrochemical gradient provide
the energy for secondary active transport of iodine
what are T3 and T4 synthesised on
thyroglobulin
what is thyroglobulin
a glycoprotein synthesised by follicular cells and released into the colloid by exocytosis
what happen s to tyrosine residues on thyroglobulin
they get iodinated by oxidised iodine (very reactive) giving monoiodotryosine (MIT) or diiodotyrosine DIT)
what does conjugation lead to
adjacent tyrosyl residues being paired together
what makes up ac colloid
thyroglobulin bound to T3 and/or T4
can the complex be taken back up into follicular cells
yes, this is where proteases liberate T3 and T4 for release into blood
how is thyroglobulin taken up into follicular cells
by endocytosis
endoscopes fuse with lysosomes, thyroglobulin is degraded liberating T3 and T4
synthesis of T3 and T4 from pituitary gland to thyroid gland
the hypothalamus releases (TRH)
causing the anterior pituitary to release TSH)
causing the thyroid gland to release thyroid hormones T3 and T4
what stimulates endocytosis of thyroglobulin into follicular cells
TSH
what stimulates release of the thyroid hormone into the bloodstream
TSH
what stimulates synthesis of thyroglobulin and Na/I transporter
TSH
what is secretion of TSH/TRH subject to
feedback regulation by T3 and T4
what proteins are T3 and T4 associated with
binding proteins in the blood
- thyroid hormone-binding globulin
- transthyretin
- albumin
do T3 and T4 have high or low solubility in water
low
is there more T3 or T4 secreted from the thyroid
more T4 (10x more)
is T3 or T4 more active
T3 is more active (up to 10x more)
what does monodeiodination in target cells do
convert much of the secreted T4 to T3
regulating cell sensitivity to thyroid hormone
what does expression diodinase enzymes do
affects the response of cells to thyroid hormone by regulating the conversion of T4 to active or inactive T3
what do deiodinase enzymes regulate
the activity of thyroid hormones
what do thyroid hormones activate
nuclear receptors
are thyroid hormones hydrophobic
yes
what do thyroid hormones require for movement across the plasma membrane
transporter proteins
what specific receptor does thyroid hormones act on
nuclear TR, a hormone sensitive transcription factor
metabolic effects of thyroid hormone
- increased BMR
- increased oxygen consumption
- increase thermogenesis
cardiovascular effects of thyroid hormone
- increased CO
- increase HR and SV
neurological effects of thyroid hormone
- enhances wakefulness
- enhances memory
- enhances alertness
- enhances reflexes
growth and developmental effects of thyroid hormone
- essential for foetal neural and bone development
- essential for normal bone growth after birth
- essential for normal tooth development
does thyroid hormone increase sensitivity of body to catecholamines
yes
what do thyroid hormones level correlate with
body weight and energy expenditure
what does hyperthyroidism cause
a hyper metabolic state
characterised by i
- increased resting energy expenditure and weight loss
-high HR and BP
what does hypothyroidism cause
- reduced resting energy expenditure
- weight gain
- lethargy and weakness
what is the basal metabolic rate
the primary source of energy expenditure in humans
